Method and apparatus to perform electrode combination selection

ABSTRACT

Approaches for selecting an electrode combination of multi-electrode pacing devices are described. Electrode combination parameters that support cardiac function consistent with a prescribed therapy are evaluated for each of a plurality of electrode combinations. Electrode combination parameters that do not support cardiac function are evaluated for each of the plurality of electrode combinations. An order is determined for the electrode combinations based on the parameter evaluations. An electrode combination is selected based on the order, and therapy is delivered using the selected electrode combination.

This application is a continuation of U.S. application Ser. No.15/240,832, filed Aug. 18, 2016, now issued as U.S. Pat. No. 9,623,252,which is a continuation of U.S. application Ser. No. 14/667,240, filedMar. 24, 2015, now U.S. Pat. No. 9,427,588, which is a continuation ofU.S. application Ser. No. 14/209,364, filed Mar. 13, 2014, now U.S. Pat.No. 9,008,775, which is a continuation of U.S. application Ser. No.14/085,398, filed Nov. 20, 2013, now U.S. Pat. No. 8,983,602, which is acontinuation of U.S. application Ser. No. 13/595,688, filed Aug. 27,2012, now U.S. Pat. No. 8,615,297, which is a continuation of U.S.application Ser. No. 11/890,668, filed Aug. 7, 2007, now U.S. Pat. No.8,265,736, the disclosures of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates generally to cardiac devices and methods,and, more particularly, to selection of one or more electrodecombinations from a plurality of electrodes.

BACKGROUND OF THE INVENTION

When functioning normally, the heart produces rhythmic contractions andis capable of pumping blood throughout the body. The heart hasspecialized conduction pathways in both the atria and the ventriclesthat enable excitation impulses (i.e. depolarizations) initiated fromthe sino-atrial (SA) node to be rapidly conducted throughout themyocardium. These specialized conduction pathways conduct thedepolarizations from the SA node to the atrial myocardium, to theatrio-ventricular node, and to the ventricular myocardium to produce acoordinated contraction of both atria and both ventricles.

The conduction pathways synchronize the contractions of the musclefibers of each chamber as well as the contraction of each atrium orventricle with the opposite atrium or ventricle. Without thesynchronization afforded by the normally functioning specializedconduction pathways, the heart's pumping efficiency is greatlydiminished. Patients who exhibit pathology of these conduction pathwayscan suffer compromised cardiac output.

Cardiac rhythm management (CRM) devices have been developed that providepacing stimulation to one or more heart chambers in an attempt toimprove the rhythm and coordination of atrial and/or ventricularcontractions. CRM devices typically include circuitry to sense signalsfrom the heart and a pulse generator for providing electricalstimulation to the heart. Leads extending into the patient's heartchamber and/or into veins of the heart are coupled to electrodes thatsense the heart's electrical signals and deliver stimulation to theheart in accordance with various therapies for treating cardiacarrhythmias and dyssynchrony.

Pacemakers are CRM devices that deliver a series of low energy pacepulses timed to assist the heart in producing a contractile rhythm thatmaintains cardiac pumping efficiency. Pace pulses may be intermittent orcontinuous, depending on the needs of the patient. There exist a numberof categories of pacemaker devices, with various modes for sensing andpacing one or more heart chambers.

A pace pulse must exceed a minimum energy value, or capture threshold,to “capture” the heart tissue, generating an evoked response thatgenerates a propagating depolarization wave that results in acontraction of the heart chamber. It is desirable for a pace pulse tohave sufficient energy to stimulate capture of the heart chamber withoutexpending energy significantly in excess of the capture threshold.Pacing in excess of a capture threshold can cause excessive energyconsumption, require premature battery replacement, and canunintentionally stimulate nerves or muscles. However, if a pace pulseenergy is too low, the pace pulses may not reliably produce acontractile response in the heart chamber and may result in ineffectivepacing that does not improve cardiac function or cardiac output.

Electrical cardiac therapies include other complexities. For example,low impedance between an anode and cathode pair can require excessiveenergy delivery, causing high energy consumption and prematurelydepleting the battery resources. In another example, excessively highimpedance between an anode and cathode pair indicates a problem with thestimulation circuit (i.e. lead damage), resulting in a lack of therapy.

Delivering electrical cardiac therapy may involve selection of anelectrode combination to which the electrical cardiac therapy isdelivered. Devices for cardiac pacing and sensing may utilize a numberof electrodes electrically coupled to the heart at one or more pacingsites, the electrodes configured to sense and/or pace a heart chamber.Each different combination of electrodes between which energy can bedelivered constitutes a vector. Pacing via multiple intra-chamberelectrode pairs may be beneficial, for example, to stimulate the hearttissue in a coordinated sequence that improves contractile function ofthe heart chamber.

The present invention provides methods and systems for selecting anelectrode combination and provides various advantages over the priorart.

SUMMARY OF THE INVENTION

The present invention involves approaches for selecting one or moreelectrode combinations. One embodiment of the invention is directed to amethod for evaluating, for each electrode combination of a plurality ofelectrode combinations, one or more first parameters produced byelectrical stimulation of the electrode combination, the firstparameters supportive of cardiac function consistent with a prescribedtherapy. In some embodiments of the present invention, a first parameteris a capture threshold.

The method for selecting an electrode combination can includeevaluating, for each electrode combination of the plurality of electrodecombinations, one or more second parameters produced by the electricalstimulation of the electrode combination, the second parameters notsupportive of cardiac function consistent with a prescribed therapy. Insome embodiments of the present invention, a second parameter isindicative of activation of extra-cardiac tissue.

The method for selecting an electrode combination can further includedetermining an order for at least some of the electrode combinations ofthe plurality of electrode combinations based on the evaluations of thefirst parameters and the second parameters. In some embodiments of thepresent invention, ordering electrode combinations can include rankingthe electrode combinations.

The method for selecting an electrode combination can further includeselecting one or more electrode combinations based on the order.Selection of the electrode combination may be done by a human orautomatically by a processor executing program instructions stored inmemory. The method can further include delivering an electricalstimulation therapy using the selected one or more electrodecombinations. Any of these method steps can be performed automaticallyby a CRM system.

Another embodiment of the invention is directed to a CRM system forselecting an electrode combination. The CRM can include a plurality ofcardiac electrodes electrically coupled respectively to a plurality ofelectrode combinations. The electrodes can further be physically coupledto an implantable housing.

According to one aspect of the present invention, the implantablehousing can contain circuitry configured to evaluate, for each electrodecombination of a plurality of electrode combinations, one or more firstparameters produced by electrical stimulation of the electrodecombination, the first parameters supportive of cardiac functionconsistent with a prescribed therapy and circuitry configured toevaluate, for each electrode combination of the plurality of electrodecombinations, one or more second parameters produced by the electricalstimulation of the electrode combination, the second parameters notsupportive of cardiac function consistent with a prescribed therapy.

The CRM system can further include an electrode combination processorconfigured to determine an order for at least some of the electrodecombinations of the plurality of electrode combinations based on theevaluations of the first parameters and the second parameters. Theelectrode combination processor can be contained within the implantablehousing, or may be contained in a patient-external housing.

The implantable housing may further include a therapy circuit configuredto deliver electrical stimulation therapy using the electrodecombinations.

The above summary of the present invention is not intended to describeeach embodiment or every implementation of the present invention.Advantages and attainments, together with a more complete understandingof the invention, will become apparent and appreciated by referring tothe following detailed description and claims taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a method of selecting an electrodecombination in accordance with embodiments of the invention;

FIG. 2 is a block diagram of a system incorporating electrodecombination selection circuitry in accordance with embodiments of theinvention;

FIG. 3 is a diagram illustrating a patient-external device that providesa user interface allowing a human analyst to interact with informationand program an implantable medical device in accordance with embodimentsof the invention;

FIG. 4 is a flowchart illustrating a method of selecting one or moreelectrode combinations based on capture threshold and phrenic nerveactivation parameters and automatically updating the electrodecombination selection in accordance with embodiments of the invention;

FIG. 5 is a flowchart illustrating a method of selecting one or moreelectrode combinations, and further exemplifying how information can behandled and managed, in accordance with embodiments of the invention;

FIG. 6 is a therapy device incorporating circuitry capable ofimplementing electrode combination selection techniques in accordancewith embodiments of the invention;

FIG. 7 shows an enlarged view of various pacing configurations that maybe used in connection with electrode combination selection in accordancewith embodiments of the invention;

FIG. 8 is a flowchart illustrating a method of estimating parameters inaccordance with embodiments of the invention;

FIG. 9 is a graph illustrating various aspects of a strength-durationplot for a parameter that supports cardiac function and astrength-duration plot for a parameter that does not support cardiacfunction that may be used to select an electrode combination for atherapeutic electrical stimulation in accordance with embodiments of theinvention;

FIG. 10 is a flowchart illustrating a method of evaluating a pluralityof electrode combinations, and further exemplifying how capturethresholds for a plurality of electrode combinations can be determined,in accordance with embodiments of the invention;

FIG. 11 is a flowchart illustrating a method of automatically updating atherapy electrode combination after an initial selection in accordancewith embodiments of the invention; and

FIG. 12 is a flowchart illustrating a method of selecting an electrodecombination, and further exemplifying ranking electrode combinations andchanging the electrode combination being used for therapy delivery usingthe ranking, in accordance with embodiments of the invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail below. It is to be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the invention isintended to cover all modifications, equivalents, and alternativesfalling within the scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

In the following description of the illustrated embodiments, referencesare made to the accompanying drawings forming a part hereof, and inwhich are shown by way of illustration, various embodiments by which theinvention may be practiced. It is to be understood that otherembodiments may be utilized, and structural and functional changes maybe made without departing from the scope of the present invention.

Systems, devices or methods according to the present invention mayinclude one or more of the features, structures, methods, orcombinations thereof described herein. For example, a device or systemmay be implemented to include one or more of the advantageous featuresand/or processes described below. It is intended that such a device orsystem need not include all of the features described herein, but may beimplemented to include selected features that provide for usefulstructures and/or functionality. Such a device or system may beimplemented to provide a variety of therapeutic or diagnostic functions.

In multi-electrode pacing systems, multiple pacing electrodes may bedisposed in a single heart chamber, in multiple heart chambers, and/orelsewhere in a patient's body. Electrodes used for delivery of pacingpulses may include one or more cathode electrodes and one or more anodeelectrodes. Pacing pulses are delivered via the cathode/anode electrodecombinations, where the term “electrode combination” denotes that atleast one cathode electrode and at least one anode electrode are used.An electrode combination may involve more than two electrodes, such aswhen multiple electrodes that are electrically connected are used as theanode and/or multiple electrodes that are electrically connected areused as the cathode. Typically, pacing energy is delivered to the hearttissue via the cathode electrode(s) at one or more pacing sites, with areturn path provided via the anode electrode(s). If capture occurs, theenergy injected at the cathode electrode site creates a propagatingwavefront of depolarization which may combine with other depolarizationwavefronts to trigger a contraction of the cardiac muscle. The cathodeand anode electrode combination that delivers the pacing energy definesthe pacing vector used for pacing. The position of the cathode relativeto cardiac tissue can be used to define an electrode combination and/ora pacing site.

Pacing pulses may be applied through multiple electrodes (i.e., pacingvectors defined by various electrode combinations) in a single cardiacchamber in a timed sequence during the cardiac cycle to improvecontractility and enhance the pumping action of the heart chamber. It isdesirable for each pacing pulse delivered via the multiple electrodecombinations to capture the cardiac tissue proximate the cathodeelectrode. The pacing energy required to capture the heart is dependenton the electrode combination used for pacing, and different electrodecombinations can have different energy requirements for capture.Particularly in the left ventricle, the minimum energy required forcapture, denoted the capture threshold, may be highly dependent on theparticular electrode combination used.

Pacing characteristics of therapy delivery using each electrodecombination of a plurality of possible electrode combinations aredependent on many factors, including the distance between theelectrodes, proximity to target tissue, type of tissue contacting andbetween the electrodes, impedance between the electrodes, resistancebetween the electrodes, and electrode type, among other factors. Suchfactors can influence the capture threshold for the electrodecombination, among other parameters. Pacing characteristics can varywith physiologic changes, electrode migration, physical activity level,body fluid chemistry, hydration, and disease state, among others.Therefore, the pacing characteristics for each electrode combination areunique, and some electrode combinations may work better than others fordelivering a particular therapy that improves cardiac functionconsistent with a prescribed therapy.

In this way, electrode combination selection should take intoconsideration at least the efficacy of one or more electrodecombinations of a plurality of electrodes in supporting cardiac functionin accordance with a prescribed therapy. The efficacy of one or moreelectrode combinations of a plurality of electrodes in supportingcardiac function in accordance with a prescribed therapy can beevaluated by consideration of one or more parameters produced byelectrical stimulation, such as capture threshold.

Electrical stimulation delivered to one body structure to produce adesired therapeutic activation may undesirably cause activation ofanother body structure. For example, electrical cardiac pacing therapycan inadvertently stimulate bodily tissue, including nerves and muscles.Stimulation of extra-cardiac tissue, including phrenic nerves, thediaphragm, and skeletal muscles, can cause patient discomfort andinterfere with bodily function.

A patient's evoked response from an electrical cardiac therapy can beunpredictable between electrode combinations. For example, an electricalcardiac therapy delivered using one electrode combination may produce anundesirable activation while an identical electrical cardiac therapydelivered using another electrode combination may not produce theundesirable activation. As such, selecting an appropriate electrodecombination, such as one electrode combination of a plurality ofelectrode combinations made possible by a multi-electrode lead thataffects the desired cardiac response with the least amount of energyconsumption and that does not unintentionally stimulate tissue, can bemany-factored and complicated.

Manually testing each parameter of interest for each possiblecathode-anode electrode combination can be a time consuming process fordoctors, clinicians, and programmers. Furthermore, it can be difficultto sort through numerous different parameters for multiple pacingelectrode combinations and understand the various tissue activationresponses of electrical therapy delivered using various electrodecombinations. Systems and methods of the present invention can simplifythese and other process.

Devices of the present invention may facilitate selection of one or moreelectrode combinations using various parameters of interest. A devicemay be preset for parameters of interest and/or a physician may selectbeneficial parameters of interest and/or non-beneficial parameters ofinterest. The parameters that are of interest can vary between patients,depending on the patient's pathology. Beneficial parameters areparameters which are associated with supported cardiac function inaccordance with a prescribed therapy and/or are the intended result of aprescribed therapy. Non-beneficial parameters are parameters which arenot associated with supported cardiac function in accordance with aprescribed therapy and/or are not the intended result of a prescribedtherapy.

The flowchart of FIG. 1 illustrates a process for selecting one or moreelectrode combinations and delivering a therapy using the one or moreselected electrode combinations. Although this method selects anelectrode combination and delivers a therapy using the electrodecombination, not all embodiments of the current invention perform all ofthe steps 110-150.

Parameters that support cardiac function are evaluated 110 for aplurality of electrode combinations.

A parameter that supports cardiac function is any parameter that isindicative of a physiological effect consistent with one or moretherapies prescribed for the patient. For example, successful capture ofa heart chamber can be indicative of cardiac contractions that arecapable of pumping blood, where ventricular pacing was a prescribedtherapy for the patient. Parameters that support cardiac functionconsistent with a prescribed therapy can be beneficial parameters, asthey can be indicative of intended therapy effects (e.g., capture).

In some embodiments of the current invention, evaluating a parameterthat supports cardiac function includes detecting whether electricaltherapy delivered through each electrode combination of a plurality ofelectrode combinations improves the patient's cardiac function,consistent with a prescribed therapy, relative to cardiac functionwithout the electrical therapy delivered using the respective electrodecombination.

Parameters that do not support cardiac function are evaluated 120 for atleast some of the plurality of electrode combinations. A parameter thatdoes not support cardiac function is any parameter that produces aphysiological effect inconsistent with the patient's prescribed therapy.

In some embodiments of the present invention, parameters that do notsupport cardiac function include parameters that are indicative ofundesirable stimulation, the undesirable stimulation not consistent witha therapy prescribed for the patient. For example, delivering anelectrical cardiac therapy using a particular electrode combination mayunintentionally stimulate skeletal muscles, causing discomfort to thepatient, not improving cardiac function consistent with a prescribedtherapy, and possibly interfering with improving cardiac function and/ordelivery of the prescribed therapy. Parameters that do not supportcardiac function consistent with a prescribed therapy can benon-beneficial parameters, as they can be indicative of unintendedeffects of the therapy.

The electrode combinations can be ordered 130. The order can be based onthe evaluations 120 and 130 of the parameters that support cardiacfunction and the parameters that do not support cardiac function.Ordering may be establishing or recognizing relationships betweenvarious electrode combinations based on parameters.

Ordering can be performed manually or automatically. For example, aclinician can consider the parameters that support cardiac function andthe parameters that do not support cardiac function and order theelectrode combinations based on the parameters. Ordering can also beperformed algorithmically by a processor executing instructions storedin memory, the processor ordering the electrode combinations based onparameter information stored in memory. For example, a data processormay algorithmically order a plurality of electrode combinations based onparameter information stored in memory, giving priority in the order toelectrode combinations that can best implement the prescribed therapywhile minimizing the occurrence of undesirable events inconsistent withthe prescribed therapy.

One or more electrode combinations can be selected 140 based on theorder of the electrode combinations. Selection of one or more electrodecombinations may be done manually by a clinician reviewing the electrodecombination order and inputting a selection into the device. Selectionmay also be done automatically, such as by a processor executinginstructions stored in memory, the processor algorithmically selectingthe electrode combination based on electrode combination orderinformation stored in memory.

After electrode combination selection, therapy can be delivered 150using the one or more selected electrode combinations. The various stepsof FIG. 1, as well as the other steps disclosed herein, can be performedautomatically, such that no direct human assistance is needed toinitiate or perform the various discrete steps.

FIG. 2 is a block diagram of a CRM device 200 that may incorporatecircuitry for selecting an electrode combination in accordance withembodiments of the present invention. The CRM device 200 includes pacingtherapy circuitry 230 that delivers pacing pulses to a heart. The CRMdevice 200 may optionally include defibrillation/cardioversion circuitry235 configured to deliver high energy defibrillation or cardioversionstimulation to the heart for terminating dangerous tachyarrhythmias.

The pacing pulses are delivered via multiple cardiac electrodes 205(electrode combinations) disposed at multiple locations within a heart,wherein a location can correspond to a pacing site. Certain combinationsof the electrodes 205 may be designated as alternate electrodecombinations while other combinations of electrodes 205 are designatedas initial electrode combinations. Two or more electrodes may bedisposed within a single heart chamber. The electrodes 205 are coupledto switch matrix 225 circuitry used to selectively couple electrodes 205of various pacing configurations to electrode combination processor 201and/or other components of the CRM device 200. The electrode combinationprocessor 201 is configured to receive information gathered via thecardiac electrodes 205 and beneficial/non-beneficial parameter sensors210. The electrode combination processor 201 can perform variousfunctions, including evaluating electrode combination parameters thatsupport cardiac function, evaluating electrode combination parametersthat do not support cardiac function, determining an order for theelectrode combinations, and selecting one or more electrode combinationsbased on the order, as well as other processes.

The control processor 240 can use patient status information receivedfrom patient status sensors 215 to schedule or initiate any of thefunctions disclosed herein, including selecting an electrodecombination. Patient status sensors 215 may include an activity monitor,a posture monitor, a respiration monitor, an oxygen level monitor, andan accelerometer, among others.

A CRM device 200 typically includes a battery power supply (not shown)and communications circuitry 250 for communicating with an externaldevice programmer 260 or other patient-external device. Information,such as data, parameter measurements, parameter evaluations, parameterestimates, electrode combination orders, electrode combinationselections, and/or program instructions, and the like, can betransferred between the device programmer 260 and patient managementserver 270, CRM device 200 and the device programmer 260, and/or betweenthe CRM device 200 and the patient management server 270 and/or otherexternal system. In some embodiments, the electrode combinationprocessor 201 may be a component of the device programmer 260, patientmanagement server 270, or other patient external system.

The CRM device 200 also includes a memory 245 for storing programinstructions and/or data, accessed by and through the control processor240. In various configurations, the memory 245 may be used to storeinformation related to activation thresholds, parameters, orders,measured values, program instructions, and the like. Parameters can bemeasured by Beneficial/Non-Beneficial Parameter Sensors 210. ParameterSensors 210 can include the various sensors discussed herein or known inthe art, including accelerometers, acoustic sensors, electrical signalsensors, pressure sensors, and the like.

FIG. 3 illustrates a patient external device 300 that provides a userinterface configured to allow a human analyst, such as a physician, orpatient, to interact with an implanted medical device. The patientexternal device 300 is described as a CRM programmer, although themethods of the invention are operable on other types of devices as well,such as portable telephonic devices, computers or patient informationservers used in conjunction with a remote system, for example. Theprogrammer 300 includes a programming head 310 which is placed over apatient's body near the implant site of an implanted device to establisha telemetry link between a CRM and the programmer 300. The telemetrylink allows the data collected by the implantable device to bedownloaded to the programmer 300. The downloaded data is stored in theprogrammer memory 365.

The programmer 300 includes a graphics display screen 320, e.g., LCDdisplay screen, that is capable of displaying graphics, alphanumericsymbols, and/or other information. For example, the programmer 300 maygraphically display one or more of the parameters downloaded from theCRM on the screen 320. The display screen 320 may includetouch-sensitive capability so that the user can input information orcommands by touching the display screen 320 with a stylus 330 or theuser's finger. Alternatively, or additionally, the user may inputinformation or commands via a keyboard 340 or mouse 350.

The programmer 300 includes a data processor 360 including softwareand/or hardware for performing the methods disclosed here, using programinstructions stored in the memory 365 of the programmer 300. In oneimplementation, sensed data is received from a CRM via communicationscircuitry 366 of the programmer 300 and stored in memory 365. The dataprocessor 360 evaluates the sensed data, which can include informationrelated to beneficial and non-beneficial parameters. The data processor360 can also perform other method steps discussed herein, includingcomparing parameters and ordering the electrode combinations, amongothers. Parameter information, electrode combination information, and anelectrode combination order, as well as other information, may bepresented to a user via a display screen 320. The parameters used forordering the electrode combinations may be identified by the user or maybe identified by the data processor 360, for example.

In some embodiments of the current invention, ordering the electrodecombinations may be determined by a user and entered via the keyboard320, the mouse 350, or stylus 330 for touch sensitive displayapplications. In some embodiments of the current invention, the dataprocessor 360 executes program instructions stored in memory to order aplurality of electrode combinations based on sensed beneficial andnon-beneficial parameters. The electrode combination order determined bythe data processor 360 is then displayed on the display screen, where ahuman analyst then reviews the order and selects one or more electrodecombinations for delivering an electrical cardiac therapy.

The flowchart of FIG. 4 illustrates a process 400 for selecting one ormore electrode combinations based on capture threshold and phrenic nerveactivation parameters and automatically updating the electrodecombination selection. The process 400 includes measuring or estimating410 a capture threshold and phrenic nerve activation threshold for eachelectrode combination at implant. The capture threshold for a particularelectrode combination may be determined by a capture threshold test. Forexample, the capture threshold test may step down the pacing energy forsuccessive pacing cycles until loss of capture is detected.

The process 400 of FIG. 4 includes measuring or estimating 410 a phrenicnerve activation threshold for each electrode combination. The phrenicnerve innervates the diaphragm, so stimulation of the phrenic nerve cancause a patient to experience a hiccup. Electrical stimulation thatcauses a hiccup can be uncomfortable for the patient, and can interferewith breathing. Additionally, phrenic nerve stimulation and/ordiaphragmatic stimulation that is inconsistent with the patient'stherapy and/or does not support cardiac function is undesirable and caninterfere with the intended therapy.

Phrenic nerve activation, and/or a phrenic nerve activation threshold,may be measured for an electrode combination by delivering electricalenergy across the electrode combination and sensing for phrenic nerveactivation. The energy delivered could also be used to simultaneouslyperform other tests, such as searching for a capture threshold. If nophrenic nerve activation is sensed using the level of electrical energydelivered, the energy level can be iteratively increased for subsequenttrials of delivering electrical energy and monitoring for phrenic nerveactivation until phrenic nerve activation is sensed. The electricalenergy level at which phrenic nerve activation is detected can be thephrenic nerve activation threshold. Alternatively, the level ofelectrical energy may be decreased or otherwise adjusted until phrenicnerve activation is not detected.

Methods for evaluating phrenic nerve activation are disclosed in U.S.Pat. Nos. 6,772,008 and 7,392,086, which are herein incorporated byreference in their respective entireties.

The process 400 of FIG. 4 further includes comparing 420 the capturethreshold and phrenic nerve activation threshold of one electrodecombination to at least one other electrode combination. Comparing canbe performed in various ways, including by a human, such as a doctor orprogrammer, or automatically by a processor executing instructionsstored in memory. In some embodiments of the present invention, someaspects of comparing 420 can be done by a human while some aspects ofcomparing 420 can be done electronically.

Comparing 420 can include comparing the capture thresholds of theelectrode combinations to one another. Such a comparison can identifywhich electrode combinations are associated with the lowest capturethresholds. Comparing 420 can also include comparing the occurrence,amounts, and/or thresholds of phrenic nerve activation of the electrodecombinations to one another. Such a comparison can identify whichelectrode combinations are associated with the highest and/or lowestoccurrence, amount and/or threshold of phrenic nerve stimulation. Otherparameters discussed herein can also be similarly compared in this andother embodiments of the present invention.

Comparing 420 can be multidimensional, such that multiple metrics arecompared for multiple electrode combinations. For example, comparing 420may consider capture threshold and phrenic nerve activation for multipleelectrode combinations to indicate which electrode combination has thelowest relative capture threshold and the least relative phrenic nerveactivation.

The process 400 of FIG. 4 further includes selecting 430 an electrodecombination based on the comparison of step 420. Selecting 430 may bedone entirely by a human, entirely by a system algorithmically, orpartially by a human and partially by the system.

Selecting 430 can be done according to criteria. For example, theresults of the comparison can be reviewed and the electrodecombination(s) matching a predetermined criterion can be selected. Thecriteria may be predefined by a human. Different sets of criteria may becreated by a human, stored in memory, and then selected by a doctor orprogrammer for use, such as use in selecting 430 an electrodecombination based on the comparison.

By way of example, selecting 430 can include selecting according to thecriteria that the selected electrode combination be the combination withthe lowest capture threshold that was not associated with phrenic nerveactivation. Other criteria that can be used additionally oralternatively include responsiveness to CRT, low energy consumption,extra-cardiac activation, dP/dt, among others indicative of beneficialparameters consistent with a prescribed therapy or non-beneficialparameters inconsistent with the prescribed therapy. The electrodecombination fitting such criteria can be identified for selection basedon the comparison 430.

The process 400 of FIG. 4 further includes delivering 440 therapy usingthe selected electrode combination. Delivering 440 therapy can includeany therapy delivery methods disclosed herein or known in the art.

The process 400 of FIG. 4 further includes determining whether anelectrode combination update is indicated 450. An electrode combinationupdate may be indicated in various ways, including detecting a conditionnecessitating an electrode combination update (such as loss of capture,change in posture, change in disease state, detection of non-therapeuticactivation, and/or short or long term change in patient activity state,for example). An electrode combination update may be initiated accordingto a predetermined schedule, or an indication given by a human orsystem.

In the particular embodiment of FIG. 4, if it is determined that anelectrode combination update is indicated 450, then the systemautomatically updates 460 the electrode combination selection 460. Invarious embodiments of the current invention, automatically updating 460electrode combination selection can include some or all of the variousmethods of the process 400 or can be based on other methods. Accordingto various embodiments of the present invention, therapy can then bedelivered 440 using the updated electrode combination. The updatedelectrode combination can be different from the electrode combinationpreviously used to deliver therapy, or the updated electrode combinationcan be the same electrode combination, despite the update.

Although the embodiment of FIG. 4 exemplified aspects of the presentinvention using capture threshold as a parameter that supports cardiacfunction consistent with a prescribed therapy, numerous other parameterscan alternatively, or additionally, be used to indicate cardiacfunction.

For example, a parameter that supports cardiac function can include adegree of responsiveness to cardiac resynchronization therapy (CRT). Asone of ordinary skill in the art would understand, when attempting CRT,it is preferable to select an electrode combination with a higher degreeof responsiveness to CRT relative to other electrode combinations.Responsiveness to CRT, including methods to detect responsiveness, isdisclosed in U.S. Patent Publication No. 2008/0177344, which is herebyincorporated by reference in its entirety.

Parameters that support cardiac function consistent with a prescribedtherapy may be related to contractility, blood pressure, dP/dt, strokevolume, cardiac output, contraction duration, hemodynamics, ventricularsynchronization, activation sequence, depolarization and/orrepolarization wave characteristics, intervals, responsiveness tocardiac resynchronization, electrode combination activation timing,stimulation strength/duration relationship, and battery consumption.

Various parameters that may be used for electrode combination selectionare discussed in U.S. Patent Publication Nos. 2010/0023078 and2008/0004667, both of which are hereby incorporated herein by referencein each respective entirety. Each of these incorporated referencesinclude parameters that support cardiac function and parameters that donot support cardiac function, the parameters usable in the methodsdisclosed herein for selecting an electrode combination.

Although the embodiment of FIG. 4 exemplified aspects of the presentinvention using phrenic nerve activation as a parameter that does notsupport cardiac function consistent with a prescribed therapy, numerousother parameters can alternatively, or additionally, be used. Parametersthat do not support cardiac stimulation consistent with a prescribedtherapy can include, but are not limited to, extra-cardiac stimulation,non-cardiac muscle stimulation (ex. skeletal muscle stimulation),unintended nerve stimulation, anodal cardiac stimulation, andexcessively high or low impedance.

For example, a parameter that does not support cardiac functionconsistent with a prescribed therapy can include skeletal muscleactivation, undesirable modes of cardiac activation, and/or undesirablenerve activation. Commonly owned U.S. Pat. No. 6,772,008, which isincorporated herein by reference, describes methods and systems that maybe used in relation to detecting undesirable tissue activation. Skeletalmuscle activation may be detected, for example, through the use of anaccelerometer and/or other circuitry that senses accelerationsindicating muscle movements that coincide with the output of thestimulation pulse.

Other methods of measuring tissue activation may involve, for example,the use of an electromyogram sensor (EMG), microphone, and/or othersensors. In one implementation, activation of the laryngeal muscles maybe automatically detected using a microphone to detect the patient'scoughing response to undesirable activation of the laryngeal muscles ornerves due to electrical stimulation.

Undesirable nerve or muscle activation may be detected by sensing aparameter that is directly or indirectly responsive to the activation.Undesirable nerve activation, such as activation of the vagus or phrenicnerves, for example, may be directly sensed using electroneurogram (ENG)electrodes and circuitry to measure and/or record nerve spikes and/oraction potentials in a nerve. An ENG sensor may comprise a neural cuffand/or other type or neural electrodes located on or near the nerve ofinterest. For example, systems and methods for direct measurement ofnerve activation signals are discussed in U.S. Pat. Nos. 4,573,481 and5,658,318 which are incorporated herein by reference in their respectiveentireties. The ENG may comprise a helical neural electrode that wrapsaround the nerve and is electrically connected to circuitry configuredto measure the nerve activity. The neural electrodes and circuitryoperate to detect an electrical activation (action potential) of thenerve following application of the electrical stimulation pulse.

Tissue activation not consistent with a prescribed therapy can alsoinclude anodal stimulation of cardiac tissue. For example, pacing maycause the cardiac tissue to be stimulated at the site of the anodeelectrode instead of the cathode electrode pacing site as expected.Cardiac signals sensed following the pacing pulse are analyzed todetermine if a pacing pulse captured the cardiac tissue. Capture viaanodal activation may result in erroneous detection of capture, loss ofcapture, unintended cardiac activation, and/or unpredictable wavepropagation. Some electrode combinations may be more susceptible toanodal stimulation than other electrode combinations. As such, theoccurrence of anodal stimulation is a non-beneficial parameter that doesnot support cardiac function and/or is not consistent with the patient'stherapy.

An exemplary list of beneficial and/or non-beneficial parameters thatmay be sensed via the parameter sensors includes impedance, contractionduration, ventricular synchronization, activation sequence,depolarization and/or repolarization wave characteristics, intervals,responsiveness to cardiac resynchronization, electrode combinationactivation timing, extra-cardiac stimulation, non-cardiac musclestimulation (ex. skeletal muscle stimulation), nerve stimulation, anodalcardiac stimulation, contractility, blood pressure, dP/dt, strokevolume, cardiac output, contraction duration, hemodynamics, ventricularsynchronization, activation sequence, depolarization and/orrepolarization wave characteristics, intervals, responsiveness tocardiac resynchronization, electrode combination activation timing,stimulation strength/duration relationship, among others. One or more ofthese sensed parameters can be used in conjunction with the methodsdiscussed herein to select an electrode combination.

The flowchart of FIG. 5 illustrates how information can be handled andmanaged according to a process 500 for selecting one or more electrodecombinations. The process 500 includes an implanted device receiving 510user information for electrode combination evaluation. The informationused for electrode combination evaluation may be determined by a human.

The process 500 of FIG. 5 further includes measuring or estimating 520electrode combination parameters identified as beneficial ornon-beneficial parameters of interest. Measuring or estimating can beperformed according to any method disclosed herein or known in the art.

By way of example, the received information may be the parameters ofbeneficial responsiveness to cardiac resynchronization andnon-beneficial arrhythmia induction, among others. The responsiveness tocardiac resynchronization parameter and the arrhythmia inductionparameter may then be measured or estimated 520 for a plurality ofelectrode combinations.

The process 500 of FIG. 5 further includes transmitting 530 electrodecombination parameter information from the pacemaker to a programmer.

The process 500 of FIG. 5 further includes displaying 540 the electrodecombination information on the programmer. The programmer can include aLCD screen or other means disclosed herein or known in the art fordisplaying information. Some or all of the electrode combinationinformation may be displayed. The electrode combination information canbe displayed as organized according to a rank, one or more groups, oneor more categories, or other information organization scheme.

For example, the plurality of electrode combinations could be ranked,the electrode combination associated with the highest relativeresponsiveness to cardiac resynchronization therapy and the lowestrelative occurrence of arrhythmia induction being ranked above electrodecombinations with lower relative responsiveness to cardiacresynchronization therapy and higher occurrence of arrhythmia induction.In this way, the electrode combinations can be ranked so as to highlightthose electrode combinations associated with the highest relative levelsof beneficial parameters and the lowest relative levels ofnon-beneficial parameters, according to a prescribed therapy.

The programmer and/or the implantable device may include a processor andexecute instructions stored in memory to algorithmically recommend oneor more electrode combinations based on the transmitted electrodecombination information. The particular recommended electrodecombination or electrode combinations can be displayed by the programmeralong with other electrode combinations and associated electrodecombination parameter information, or the recommended electrodecombination or electrode combinations may be displayed by the programmerwith electrode combinations that were not recommended. The programmermay display one or more recommend electrode combinations andnon-recommended electrode combinations, and visually highlight the oneor more recommended electrode combinations. The programmer may displayone or more recommended electrode combinations amongst other electrodecombinations, but order the one or more recommended electrodecombinations to indicate which electrode combination or combinations arerecommended.

In addition to recommending an electrode combination and displaying therecommended electrode combination, the programmer may also give reasonswhy the particular electrode combination or combinations wererecommended.

Although the particular process 500 of FIG. 5 states that the programmerdisplays the electrode combination information, other implementationsare possible. For example, the electrode combination information may bedisplayed on a screen or printed from a device remote from theprogrammer.

Inputting 550 the electrode combination selection may be facilitated bya device displaying the electrode combination information, such as by auser selecting or confirming a displayed recommended electrodecombination. Inputting 550 may be done by any methods disclosed hereinor known in the art. In some embodiments of the invention, severalelectrode combination selections can be input by the user to theprogrammer.

The process 500 of FIG. 5 further includes the programmer 560 uploadingan electrode combination selection to a pacemaker. The pacemaker of step560 could be the implanted device of step 510. Uploading can befacilitated by the same means used to facilitate the implanted devicereceiving the user criteria, and/or transmitting the electrodecombination parameter information.

The therapy device 600 illustrated in FIG. 6 employs circuitry capableof implementing the electrode combination selection techniques describedherein. The therapy device 600 includes CRM circuitry enclosed within animplantable housing 601.

The CRM circuitry is electrically coupled to an intracardiac lead system610. Although an intracardiac lead system 610 is illustrated in FIG. 6,various other types of lead/electrode systems may additionally oralternatively be deployed. For example, the lead/electrode system maycomprise and epicardial lead/electrode system including electrodesoutside the heart and/or cardiac vasculature, such as a heart sock, anepicardial patch, and/or a subcutaneous system having electrodesimplanted below the skin surface but outside the ribcage.

Portions of the intracardiac lead system 610 are inserted into thepatient's heart. The lead system 610 includes cardiac pace/senseelectrodes 651-656 positioned in, on, or about one or more heartchambers for sensing electrical signals from the patient's heart and/ordelivering pacing pulses to the heart. The intracardiac sense/paceelectrodes 651-656, such as those illustrated in FIG. 6, may be used tosense and/or pace one or more chambers of the heart, including the leftventricle, the right ventricle, the left atrium and/or the right atrium.The CRM circuitry controls the delivery of electrical stimulation pulsesdelivered via the electrodes 651-656. The electrical stimulation pulsesmay be used to ensure that the heart beats at a hemodynamicallysufficient rate, may be used to improve the synchrony of the heartbeats, may be used to increase the strength of the heart beats, and/ormay be used for other therapeutic purposes to support cardiac functionconsistent with a prescribed therapy.

The lead system 610 includes defibrillation electrodes 641, 642 fordelivering defibrillation/cardioversion pulses to the heart.

The left ventricular lead 605 incorporates multiple electrodes 654 a-654d and 655 positioned at various locations within the coronary venoussystem proximate the left ventricle. Stimulating the ventricle atmultiple locations in the left ventricle or at a single selectedlocation may provide for increased cardiac output in a patientssuffering from congestive heart failure (CHF), for example, and/or mayprovide for other benefits.

Electrical stimulation pulses may be delivered via the selectedelectrodes according to a timing sequence and output configuration thatenhances cardiac function. Although FIG. 6 illustrates multiple leftventricle electrodes, in other configurations, multiple electrodes mayalternatively or additionally be provided in one or more of the rightatrium, left atrium, and right ventricle.

Portions of the housing 601 of the implantable device 600 may optionallyserve as one or more multiple can 681 or indifferent 682 electrodes. Thehousing 601 is illustrated as incorporating a header 689 that may beconfigured to facilitate removable attachment between one or more leadsand the housing 601. The housing 601 of the therapy device 600 mayinclude one or more can electrodes 681. The header 689 of the therapydevice 600 may include one or more indifferent electrodes 682. The can681 and/or indifferent 682 electrodes may be used to deliver pacingand/or defibrillation stimulation to the heart and/or for sensingelectrical cardiac signals of the heart.

Communications circuitry is disposed within the housing 601 forfacilitating communication between the CRM circuitry and apatient-external device, such as an external programmer or advancedpatient management (APM) system. The therapy device 600 may also includesensors and appropriate circuitry for sensing a patient's metabolic needand adjusting the pacing pulses delivered to the heart and/or updatingthe electrode combination selection to accommodate the patient'smetabolic need. In some implementations, an APM system may be used toperform some of the processes discussed here, including evaluating,estimating, comparing, ordering, selecting, and updating, among others.Methods, structures, and/or techniques described herein, may incorporatevarious APM related methodologies, including features described in oneor more of the following references: U.S. Pat. Nos. 6,221,011;6,270,457; 6,277,072; 6,280,380; 6,312,378; 6,336,903; 6,358,203;6,368,284; 6,398,728; and 6,440,066, which are hereby incorporatedherein by reference in each of their respective entireties.

In certain embodiments, the therapy device 600 may include circuitry fordetecting and treating cardiac tachyarrhythmia via defibrillationtherapy and/or anti-tachyarrhythmia pacing (ATP). Configurationsproviding defibrillation capability may make use of defibrillation coils641, 642 for delivering high energy pulses to the heart to terminate ormitigate tachyarrhythmia.

CRM devices using multiple electrodes, such as illustrated herein, arecapable of delivering pacing pulses to multiple sites of the atriaand/or ventricles during a cardiac cycle. Certain patients may benefitfrom activation of parts of a heart chamber, such as a ventricle, atdifferent times in order to distribute the pumping load and/ordepolarization sequence to different areas of the ventricle. Amulti-electrode pacemaker has the capability of switching the output ofpacing pulses between selected electrode combinations within a heartchamber during different cardiac cycles.

FIG. 7 illustrates an enlarged view of the area delineated by the dashedline circle in FIG. 6. FIG. 7 illustrates various pacing configurations754 a, 754 b, 754 c, 754 d, 754 cd, and 756 that may be used to deliverpacing pulses. Each of the pacing configurations 754 a, 754 b, 754 c,754 d, 754 cd, and 756 includes a common cathode electrode 655. Pacingconfiguration 754 a is defined between cathode electrode 655 and anodeelectrode 654 a; pacing configuration 754 b is defined between cathodeelectrode 655 and anode electrode 654 b; pacing configuration 754 c isdefined between cathode electrode 655 and anode electrode 654 c; pacingconfiguration 754 d is defined between cathode electrode 655 and anodeelectrode 654 d; pacing configuration 756 is defined between cathodeelectrode 655 and anode electrode 656. In some configurations, thepacing configuration cathode, or the pacing configuration anode, orboth, may comprise multiple electrodes. For example, pacingconfiguration 754 cd includes cathode electrode 655 and anode electrodes654 c and 654 d.

Each of the pacing configurations discussed above correspond to anelectrode combination, and each pacing configuration and electrodecombination likewise correspond to a pacing site and/or vector.Delivering an identical electrical therapy using each electrodecombination can elicit a different response from the patient. Forexample, therapy delivered at one electrode combination may be morelikely to capture a chamber than another site. Also, therapy deliveredusing one electrode combination may be more likely to stimulate thediaphragm than another site. Therefore, it is important to identify theelectrode combination through which optimum therapy can be delivered. Insome cases, the optimum electrode combination for therapy is one thatcauses the desired response, using the smallest amount of power (such asbattery storage), that does not cause undesirable stimulation. Forexample, an optimal electrode combination may be an electrodecombination through which a delivered therapy captures the intendedchamber requiring the smallest amount of voltage and current that doesnot stimulate the diaphragm or skeletal muscles, or other extra-cardiactissue.

The flowchart of FIG. 8 illustrates a process 800 for estimatingparameters, specifically, both beneficial (e.g., capture) andnon-beneficial (e.g., undesirable activation) parameters. The process800 includes measuring 810 a capture threshold of an initial electrodecombination. The procedure for measuring 810 a capture threshold for theinitial electrode combination can be done according to any capturethreshold measuring methods disclosed herein or known in the art.

The process 800 of FIG. 8 further includes measuring 820 the impedanceof the initial electrode combination. The impedance of the initialelectrode combination may be measured with the capture thresholdmeasurement of the initial electrode combination. Any method formeasuring impedance for each electrode combination may be used. Oneillustrative example of techniques and circuitry for determining theimpedance of an electrode combination is described in commonly ownedU.S. Pat. No. 6,076,015 which is incorporated herein by reference in itsentirety.

In accordance with this approach, measurement of impedance involves anelectrical stimulation source, such as an exciter. The exciter deliversan electrical excitation signal, such as a strobed sequence of currentpulses or other measurement stimuli, to the heart between the electrodecombination. In response to the excitation signal provided by anexciter, a response signal, e.g., voltage response value, is sensed byimpedance detector circuitry. From the measured voltage response valueand the known current value, the impedance of the electrode combinationmay be calculated.

The process 800 of FIG. 8 further includes measuring 830 the impedanceof an alternate electrode combination. The measuring step 830 could berepeated for a plurality of different alternate electrode combinations.

The process 800 of FIG. 8 further includes measuring 840 an undesirableactivation threshold of the initial electrode combination. The procedurefor measuring 840 the undesirable activation threshold of the initialelectrode combination may be similar to the procedure for measuring 810the capture threshold of the initial electrode combination, and may bedone concurrently with the measuring 810 of the capture threshold of theinitial electrode combination.

Undesirable activation threshold measuring may be performed byiteratively increasing, decreasing, or in some way changing a voltage,current, duration, and/or some other therapy parameter between a seriesof test pulses that incrementally increase in energy level. One or moresensors can monitor for undesirable activation immediately after eachtest pulse is delivered. Using these methods, the point at which aparameter change causes undesirable activation can be identified as anundesirable activation threshold.

By way of example and not by way of limitation, the undesirableactivation threshold for an electrode combination may be measured bydelivering first test pulse using the initial electrode combination.During and/or after each test pulse is delivered, sensors can monitorfor undesirable activation. For example, an accelerometer may monitorfor contraction of the diaphragm indicating that the test pulsestimulated the phrenic nerve and/or diaphragm muscle. If no phrenicnerve and/or diaphragm muscle activation is detected after delivery of atest pulse, then the test pulse is increased a predetermined amount andanother test pulse is delivered. This scanning process of delivering,monitoring, and incrementing is repeated until phrenic nerve and/ordiaphragm muscle activation is detected. One or more of the test pulseenergy parameters at which the first undesirable activation is detected,such as voltage, can be considered to be the undesirable activationthreshold.

The process 800 of FIG. 8 further includes estimating 850 a capturethreshold of the alternate electrode combination. Estimating 850 thecapture threshold of the alternate electrode combination can beperformed by using the capture threshold and the impedance of theinitial electrode combination and the impedance of the alternateelectrode combination.

Estimation of the capture threshold of the alternate electrodecombination in accordance with some embodiments described herein isbased on the assumption that for a given pulse width, the capturethreshold voltage for the initial electrode combination and the capturethreshold voltage for the alternate electrode combination require anequal amount of current, energy or charge. The relationship between thecapture threshold voltage and current for each electrode combination canbe defined by Ohm's law as follows:V_(th)=I_(th)Z,  [1]

where V_(th) is the capture threshold voltage of the electrodecombination, I_(th) is the capture threshold current of the electrodecombination, and Z is the impedance of the electrode combination.

For the initial electrode combination, the relationship between thecapture threshold voltage and current may be expressed as:V_(th-in)=I_(th-in)Z_(in)  [2]

where, V_(th-in) is the capture threshold voltage of the initialelectrode combination, I_(th-in) is the capture threshold current of theinitial electrode combination, and Z_(in) is the impedance of theinitial electrode combination.

For the alternate electrode combination, the relationship between thecapture threshold voltage and current may be expressed as:V_(th-ex)=I_(th-ex)Z_(ex)  [3]where, V_(th-ex) is the capture threshold voltage of the alternateelectrode combination, I_(th-ex) is the capture threshold current of thealternate electrode combination, and Z_(ex) is the impedance of thealternate electrode combination.

As previously stated, in some embodiments, the capture threshold currentof two electrode combinations having a common electrode is assumed to beabout equal, or, I_(th-in)=I_(th-ex).

The relationship between the alternate and initial capture thresholdvoltages may then be expressed as:

$\begin{matrix}{V_{{th} - {ex}} = {\frac{V_{{th} - {in}}}{Z_{in}}Z_{ex}}} & \lbrack 4\rbrack\end{matrix}$

By the processes outlined above V_(th-in), Z_(in), and, Z_(ex) aremeasured parameters, and the capture threshold voltage may be estimatedbased on these measured parameters.

The accuracy of an estimation calculation of a capture threshold for aparticular electrode combination may be increased if the measuredelectrode combination has the same polarity as the electrode combinationfor which the capture threshold is being estimated. Methods forparameter estimation, including capture threshold estimation, aredisclosed in U.S. Pat. No. 7,680,536, herein incorporated by referencein its entirety.

The process 800 of FIG. 8 further includes estimating 860 an undesirableactivation threshold of the alternate electrode combination. Estimating860 the undesirable activation threshold of the alternate electrodecombination can be performed by using the undesirable activationthreshold and the impedance of the initial electrode combination and theimpedance of the alternate electrode combination. Estimating 850 theundesirable activation threshold of the alternative electrodecombination can be performing using methods similar to estimating acapture threshold, as discussed and referenced herein.

Estimating a threshold, such as estimating a capture threshold and/or anundesirable activation threshold, instead of measuring the same, canprovide several advantages. For example, in some circumstances,measuring and estimating of some thresholds for a plurality of electrodecombinations can be done faster than measuring the threshold for eachelectrode combination of the plurality of electrode combinations, as oneor more test pulses do not need to be delivered for each electrodecombination. Additionally, a test pulse can be uncomfortable for apatient to experience, and therefore minimizing the number of testpulses can be preferable.

Appropriate selection of the energy parameters and an electrodecombination that produce the desired activation that supports cardiacand avoid the undesirable activation, consistent with a prescribedtherapy, can involve the use of strength-duration relationships measuredor otherwise provided. The selection of an electrode combination mayinvolve evaluating the cardiac response across ranges of one or more ofpulse width, pulse amplitude, frequency, duty cycle, pulse geometry,and/or other energy parameters.

Capture is produced by pacing pulses having sufficient energy to producea propagating wavefront of electrical depolarization that results in acontraction of the heart tissue. The energy of the pacing pulse is aproduct of two energy parameters—the amplitude of the pacing pulse andthe duration of the pulse. Thus, the capture threshold voltage over arange of pulse widths may be expressed in a strength-duration plot 910as illustrated in FIG. 9.

Undesirable activation by a pacing pulse is also dependent on the pulseenergy. The strength-duration plot 920 for undesirable activation mayhave a different characteristic from the capture strength-duration andmay have a relationship between pacing pulse voltage and pacing pulsewidth.

A CRM device, such as a pacemaker, may have the capability to adjust thepacing pulse energy by modifying either or both the pulse width and thepulse amplitude to produce capture. Identical changes in pacing pulseenergy may cause different changes when applied to identical therapiesusing different electrode combinations. Determining a strength-durationplot 910 for a plurality of electrode combinations can aid in selectingan electrode combination, as the strength-duration plots can be a basisfor comparison of beneficial and non-beneficial pacing characteristicsand parameters.

FIG. 9 provides graphs illustrating a strength-duration plot 910associated with capture and a strength-duration plot 920 associated withan undesirable activation. A pacing pulse having a pulse width of W₁requires a pulse amplitude of V_(c1) to produce capture. A pacing pulsehaving pulse width W₁ and pulse amplitude V_(c1) exceeds the voltagethreshold, V_(u1), for an undesirable activation. If the pulse width isincreased to W₂, the voltage required for capture, V_(c2), is less thanthe voltage required for undesirable activation, V_(u2). Therefore,pacing pulses can be delivered at the pacing energy associated with W₂,V_(c2) to provide capture of the heart without causing the undesirableactivation. The shaded area 950 between the plots 910, 920 indicates theenergy parameter values that may be used to produce capture and avoidundesirable activation.

If multiple-point strength duration plots are known for capture andundesirable activation, the energy parameters for a particular electrodecombination may be determined based on these two plots. For example,returning to FIG. 9, the area 950 to the right of the intersection 951of the strength-duration plots 910, 920 defines the set of energyparameter values that produce capture while avoiding undesirablestimulation. Energy parameter values that fall within this region 950,or within a modified region 960 that includes appropriate safety marginsfor pacing 961 and undesirable activation 962, may be selected.

According to some embodiments of the present invention, variousparameters and/or characteristics, such as ranges, windows, and/orareas, of the plots of FIG. 9 may be used in selecting an electrodecombination. For example, equivalent strength-duration plots 910 andstrength-duration plot 920 associated with an undesirable activation maybe generated for each of a plurality of electrode combinations. Then therespective areas 960 and/or 950 may be compared between the electrodecombinations, the comparison used to determine an order for theelectrode combinations. Because the parameters represented by area 960represent the available ranges of voltage and pulse width within anacceptable safety margin, electrode combinations with relatively largearea 960 may be favorably ranked in an electrode combination order. Acomparison can also be made between various electrode combinations ofthe voltage ranges, at a specific pulse width, that captures the heartwithout causing undesirable stimulation, with priority in the orderbeing given to electrode combinations with the largest ranges.

Strength-duration plots, such as plots 910 and 920, can provide otherparameters for evaluating and comparing to order electrode combinationsand select an electrode combination. For example, criteria for selectingan electrode combination may specify that the selected combination isthe combination with the lowest capture threshold that does not exceed acertain pulse width.

Methods and systems for determining and using strength-durationrelationships are described in U.S. Patent Publication No. 2008/0071318,which is incorporated herein by reference in its entirety.

The flowchart of FIG. 10 illustrates a process 1000 for determiningcapture thresholds for a plurality of electrode combinations. Theprocess 1000 includes initiating 1010 a step down threshold test, andsetting an initial pacing energy. The process 1000 further includesdelivering 1020 a pacing pulse at pacing energy to an electrodecombination. The electrode combination may be an initial electrodecombination. The pacing energy may be the initial pacing energy,particularly in the case where step 1020 has not been previouslyperformed.

After delivery 1020 of the pacing pulse, the process monitors todetermine whether loss of capture is detected 1030. If loss of captureis detected, then the process 1000 proceeds to determining 1040 otherbeneficial parameters, and storing the beneficial parameter information.The other beneficial parameters determined could be any of thebeneficial parameters discussed herein or known in the art that supportcardiac function consistent with a prescribed therapy. Examples of suchbeneficial parameters include electrode combination responsiveness toCRT, low battery consumption, and cardiac output, among otherparameters.

The process determines 1060 non-beneficial parameters, and stores thenon-beneficial parameter information. The non-beneficial parametersdetermined could be any of the non-beneficial parameters discussedherein or known in the art. Examples of such non-beneficial parametersinclude extra-cardiac stimulation and anodal stimulation, among otherparameters.

After determining 1060 non-beneficial parameters, the process 1000proceeds to decrease 1070 the electrode combination energy. After theelectrode combination energy is decreased 1070, a pacing pulse isdelivered 1020 using the electrode combination using the energy level towhich the energy level was decreased. In this way, steps 1020, 1030,1040, 1060, and 1070 can be repeated, decreasing 1070 the pacing energyfor the electrode combination until loss of capture is detected 1030. Assuch, steps 1010, 1020, 1030, 1040, 1060, and 1070 can scan for acapture threshold, the capture threshold being stored 1050 in memory forthe electrode combination once it has been identified by a detected lossof capture 1030.

After detecting loss of capture 1030 and storing 1050 the capturethreshold for the electrode combination, the process 1000 evaluateswhether there are more electrode combinations to test 1090. If there aremore electrode combinations to test, then the process 1000 switches 1080to the next electrode combination and repeats steps 1020, 1030, 1040,1060, and 1070 to determine the capture threshold for the next electrodecombination. When there are no more electrode combinations to test 1090,the test ends 1095. As such, process 1000 can be used to determine thecapture threshold, beneficial parameters, and non-beneficial parametersfor one or more of a plurality of electrode combinations. Thisinformation can then be used in conjunction with other methods disclosedherein to select an electrode combination, among other things.

Although the process 1000 of FIG. 10 used a step down capture thresholdtest, in other implementations, the capture threshold test may involve astep-up capture threshold test, a binary search test, or may involveother capture threshold testing methods as are known in the art. Similarmethods to those discussed herein can be used to determine otherparameter thresholds.

The capture threshold of an electrode combination may change over timedue to various physiological effects. Testing the capture threshold fora particular electrode combination may be implemented periodically or oncommand to ensure that the pacing energy delivered to the particularelectrode combination remains sufficient to produce capture.

The flowchart of FIG. 11 illustrates a process 1100 for automaticallyupdating a therapy electrode combination after an initial selection.Beneficial parameters and non-beneficial parameters are measured orestimated 1110 for a plurality of electrode combinations. Step 1110 canbe scheduled to occur at implant, or could be initiated after implant.As in other embodiments discussed herein, the beneficial parameters canbe parameters that support cardiac function consistent with a prescribedtherapy and the non-beneficial parameters can be parameters that do notsupport cardiac function consistent with a prescribed therapy.

After the beneficial and non-beneficial parameters are evaluated 1110,the beneficial and non-beneficial parameters are compared 1120. Based onthe comparison, electrode combinations are selected 1130. Therapy isthen delivered 1140 using the selected electrode combinations. Aftertherapy is delivered 1140 using the selected electrode combinations, theprocess 1100 evaluates whether a periodic update is required 1150. Aperiodic update could be mandated by a programmed update schedule, ormay be performed upon command.

If no periodic update is required, then therapy continues to bedelivered 1140 using the selected electrode combinations. However, if aperiodic update is required, then the process automatically re-measuresor re-estimates 1160 beneficial and non-beneficial parameters for theplurality of electrode combinations. Automatically re-measuring orre-estimating 1160 could be performed by a method similar or identicalto the method used to measure or estimate beneficial parameters 1110 atimplant. After re-measuring or re-estimating the beneficial andnon-beneficial parameters, the re-measured or re-estimated parametersare compared 1120, such that electrode combinations may then be selected1130 and used to deliver 1140 a therapy.

The flowchart of FIG. 12 illustrates a process 1200 for rankingelectrode combinations and changing the electrode combination being usedfor therapy delivery using the ranking. The process 1200 begins withmeasuring or estimating 1210 beneficial parameters and non-beneficialparameters for a plurality of electrode combinations. As in otherembodiments discussed herein, the beneficial parameters can beparameters that support cardiac function consistent with a prescribedtherapy and the non-beneficial parameters can be parameters that do notsupport cardiac function consistent with a prescribed therapy.

After the beneficial and non-beneficial parameters are measured orestimated 1210, the beneficial and non-beneficial parameters are ranked1220.

Ranking can include establishing a hierarchical relationship between aplurality of electrode combinations based on parameters. In suchembodiments, the highest ranked electrode combination maybe theelectrode combination with most favorable beneficial parameter andnon-beneficial parameter values relative to other electrodecombinations, which are likewise ordered in a rank.

Based on the ranking, electrode combinations are selected 1230. Therapyis then delivered 1240 using the selected electrode combinations.

After therapy is delivered 1240 using the selected electrodecombinations, the process 1200 senses 1250 for one or more conditionsindicative of a change in the patient's status. In some embodiments ofthe invention, a sensed change in the patient status could include asensed change in activity level, posture, respiration, electrodeposition, body fluid chemistry, blood or airway oxygen level, bloodpressure, hydration, hemodynamics, or electrode combination impedance,among other events.

If no status change is detected 1260, then therapy continues to bedelivered 1240 using the selected electrode combinations. However, if astatus change is detected 1260, then the process selects 1270 the nextranked electrode combination or sites for therapy delivery and delivers1240 therapy via the selected site or sites. According to the particularprocess 1200 of FIG. 12, no re-measuring or re-estimating of parametersis needed, as the process uses the ranking determined in step 1220.

Although the embodiment of FIG. 12 uses a ranking method to order theelectrode combinations, other ordering methods are contemplated withinthe scope of the present invention. Ordering may include grouping,attributing, categorizing, or other processes that are based onparameter evaluations.

Ordering can include grouping a plurality of electrode combinationsaccording to one or more of the parameters that support cardiac functionand one or more of the parameters that do not support cardiac function,consistent with a prescribed therapy. For example, the electrodecombinations of the plurality of electrode combinations can be groupedin various categories, each category associated with a different type ofdetected undesirable stimulation (ex. phrenic nerve, anodal stimulation,excessive impedance) and/or parameter that does support cardiac function(ex. low capture threshold; low impedance).

In some applications, it is desirable to select pacing electrodes basedon a number of interrelated parameters. For example, in cardiacresynchronization therapy (CRT) which involves left ventricular pacing,it is desirable to deliver pacing pulses that capture the heart tissueto produce a left ventricular contraction without unwanted stimulationto other body structures. However, the pacing therapy may be ineffectiveor less effective if pacing is delivered to a site that is anon-responder site to CRT. Thus, selection of a responder site fortherapy delivery should also be taken into account. In some embodiments,the electrode selection may consider several inter-related parameters,ordering, ranking, grouping and/or recommending the electrodecombinations to achieve specific therapeutic goals.

In some embodiments, the ordering, ranking, grouping and/or recommendingmay be performed using a multivariable optimization procedure. Electrodeselection using some level of algorithmic automaticity is particularlyuseful when a large number of electrode combinations are possible inconjunction with the evaluation of several parameters.

Ordering can be based on the evaluations of any number of differentparameters that support cardiac function consistent with a prescribedtherapy and any number of parameters that do not support cardiacfunction consistent with a prescribed therapy. For example, ordering canbe based on a comparison of the respective evaluations of two differentparameters that each support cardiac function consistent with aprescribed therapy and one or more parameters that do not supportcardiac function consistent with a prescribed therapy, each evaluationconducted for each electrode combination of a plurality of electrodecombinations. In this example, the two different parameters that supportcardiac function consistent with a prescribed therapy could be leftventricular to capture threshold and improved hemodynamics, while theparameter that does not support cardiac function consistent with aprescribed therapy could be phrenic nerve activation.

Evaluating, ordering, and other comparisons of the present inventionbased on multiple parameters can include one, two, three, four, five, ormore different parameters that support cardiac function consistent witha prescribed therapy and one, two, three, four, five, or more differentparameters that do not support cardiac function consistent with aprescribed therapy.

In some embodiments of the invention, not all possible electrodecombinations will be evaluated. For example, a very high capturethreshold associated with a first electrode combination may indicatethat another electrode combination using the cathode or the anode of thefirst electrode combination may as well have a very high capturethreshold. In such cases, evaluations of parameters for electrodecombinations using those electrodes and/or electrodes proximate one ofthose electrodes will not be conducted. Forgoing evaluation of thoseelectrode combinations likely to perform poorly based on the performanceof similar electrode combinations can save evaluation time, energy, andavoid unnecessary stimulation while testing patient response. Theforgoing of evaluating certain electrode combinations can be based onany of the other parameters discussed herein.

The components, functionality, and structural configurations depictedherein are intended to provide an understanding of various features andcombination of features that may be incorporated in an implantablepacemaker/defibrillator. It is understood that a wide variety of cardiacmonitoring and/or stimulation device configurations are contemplated,ranging from relatively sophisticated to relatively simple designs. Assuch, particular cardiac device configurations may include particularfeatures as described herein, while other such device configurations mayexclude particular features described herein.

Various modifications and additions can be made to the preferredembodiments discussed hereinabove without departing from the scope ofthe present invention. Accordingly, the scope of the present inventionshould not be limited by the particular embodiments described above, butshould be defined only by the claims set forth below and equivalentsthereof.

What is claimed is:
 1. A method for identifying an electrode combinationfor use in providing a patient therapy using one or moremultiple-electrode leads, the method comprising: evaluating, using anelectrode combination processor, for each electrode combination of aplurality of electrode combinations, one or more patient parametersassociated with electrical stimulation of a particular electrodecombination; ordering, using the electrode combination processor, theplurality of electrode combinations into an electrode combination orderusing the one or more evaluated patient parameters; and providing, usingthe electrode combination processor, information about the one or moreevaluated patient parameters in the electrode combination order.
 2. Themethod of claim 1, wherein the ordering the plurality of electrodecombinations includes assigning a rank to each of the plurality ofelectrode combinations using the one or more evaluated patientparameters, wherein the rank indicates a preference for a particularelectrode combination to carry out a prescribed patient therapy.
 3. Themethod of claim 1, further comprising receiving a selection of one ofthe electrode combinations using the information about the one or moreparameters, and programming an implantable pacing circuit to deliver apacing therapy using the selected one of the electrode combinations. 4.The method of claim 1, further comprising updating a therapy signaldelivery parameter in an implantable pacing circuit using the electrodecombination order.
 5. The method of claim 1, further comprisingdisplaying, using a display screen, information about the one or moreevaluated patient parameters in the electrode combination order.
 6. Themethod of claim 1, wherein the evaluating includes, for each electrodecombination of the plurality of electrode combinations, evaluating firstparameters that support cardiac function consistent with a prescribedpatient therapy and evaluating second parameters that do not supportcardiac function consistent with the prescribed patient therapy.
 7. Themethod of claim 6, wherein the ordering includes using the first and thesecond parameters.
 8. The method of claim 6, wherein the evaluatingsecond parameters that do not support cardiac function includesdetermining a presence or absence of phrenic nerve stimulation for eachof electrode combination of the plurality of electrode combinations. 9.The method of claim 1, wherein the evaluating the one or more patientparameters includes evaluating a cardiac capture threshold for each ofthe electrode combinations, and evaluating extra-cardiac stimulation foreach of the electrode combinations.
 10. The method of claim 1, whereinthe evaluating the one or more patient parameters includes evaluating aresponsiveness to a cardiac resynchronization therapy.
 11. The method ofclaim 1, wherein the evaluating the one or more patient parametersincludes detecting at least one of unintended nerve stimulation andunintended muscle stimulation.
 12. The method of claim 1, furthercomprising performing an electrode combination status update, includingre-evaluating the one or more patient parameters for at least a selectedone of the electrode combinations.
 13. The method of claim 1, whereinthe evaluating the one or more patient parameters for each electrodecombination of the plurality of electrode combinations includesevaluating one or more of an impedance, contraction duration,ventricular synchronization, activation sequence, depolarization and/orrepolarization wave characteristic, interval, responsiveness to cardiacresynchronization, activation timing, extra-cardiac stimulation,non-cardiac muscle stimulation, nerve stimulation, anodal cardiacstimulation, contractility, blood pressure, change in pressure overtime, stroke volume, cardiac output, contraction duration, hemodynamicparameters, ventricular synchronization, activation sequence, anddepolarization and/or repolarization wave characteristics.
 14. A cardiacrhythm management system comprising: an electrode combination processorcircuit configured to: evaluate, for each electrode combination of aplurality of electrode combinations, one or more patient parametersassociated with electrical stimulation of a particular electrodecombination; order the plurality of electrode combinations into anelectrode combination order using the one or more evaluated patientparameters; and provide information about the one or more evaluatedpatient parameters in the electrode combination order.
 15. The system ofclaim 14, further comprising an external device in data communicationwith the electrode combination processor circuit, wherein the externaldevice includes a display configured to display information about theone or more evaluated patient parameters in the electrode combinationorder.
 16. The system of claim 15, wherein the external device comprisesa user input configured to receive a user selection of at least one ofthe electrode combinations using the information about the one or moreparameters.
 17. The system of claim 14, further comprising a therapydelivery circuit configured to deliver a cardiac resynchronizationtherapy using a selected one of the plurality of electrode combinations.18. The system of claim 14, further comprising at least one leadincluding at least four discrete electrodes, and wherein the electrodecombination processor circuit is configured to evaluate the one or morepatient parameters using different combinations of the at least fourdiscrete electrodes.
 19. A cardiac rhythm management system comprising:an electrode combination processor circuit configured to: evaluate, foreach of multiple electrode combinations available for use by the cardiacrhythm management system, one or more first parameters and one or moresecond parameters produced as a result of an electrical stimulationdelivered using each of the multiple electrode combinations, the firstparameters supportive of cardiac function consistent with a prescribedtherapy and the second parameters not supportive of cardiac functionconsistent with the prescribed therapy; compare the first and secondparameters for each of the evaluated multiple electrode combinations;select for use, for a first therapy duration, a first electrodecombination from the multiple electrode combinations using a result ofthe compared parameters; and a therapy circuit configured to deliver acardiac resynchronization therapy using the selected first or secondelectrode combinations.
 20. The system of claim 19, further comprising aprogrammer device including a display and a user input, wherein theelectrode combination processor circuit is further configured to orderthe evaluated multiple electrode combinations using the first and secondparameters as compared, and wherein the programmer device is configuredto display the evaluated multiple electrode combinations and receive anindication from a user, using the user input, of a selected one of theelectrode combinations for use in the cardiac resynchronization therapy.